Mortality of USA dialysis patients is higher than that observed in Western Europe and Japan when appropriate adjustments are made for demographic and disease characteristics Many published reports state that underdialysis is rampant in the U.S. using as a comparative standard the only randomized trial which controlled dialysis dose, time on dialysis and provided information on dietary protein intake (The National Coopera- tive Dialysis Study). While degree of underdialysis (expressed as Kt/V less than 0.8) correlates with increased mortality, little information is available on the effect of new doses of dialysis (e.g. Kt/V 1.5) on survival. Similarly, the effects of new synthetic dialysis membranes, which are biocompatible and have the ability to remove molecules much larger than those removed by the cellulosic membranes currently used, is also not clearly understood. Consequently there is urgent need for a randomized controlled trial of: 1. Different levels of dialytic treatment, 2. Effects of membranes of different permeability (high flux vs. low flux), 3. Effects of membranes of different biocompatibility. Outcomes to be evaluated include mortality signs and symptoms, biochemical measures bearing on morbidity and quality of life. A properly constructed trial will provide guidelines for the appropriate prescription of dialysis while simultaneously adding to our knowledge of end stage renal disease and its treatment. This could improve survival of patients in this population and reduce current mortality associated with treatment. The trial must be multicenter, randomized and deal with patients representative of the U.S. dialysis population. Problems such as definition and measurement of adequacy, choice of membrane, reprocessing methods and the effects of prior treatment must be considered in the formulation of the experimental design. The initial design period will take into account these problems. The subsequent period will deal with attempts to randomize patients into the selected therapeutic groups. This will be followed by an analysis preceding the definitive long term trial which will provide guidance on the dialysis treatment for the future.